Magnesium oxychloride cement mix and method of making



Patented Mar. 6, 1951 AND METHOD OF MAKING William C. Eastin, Palo Alto, Calif.,-assignor to Food Machinery and Chemical Corporation, Wilmington, Del., a corporationofDelaware No Drawing. Application September 1, 1945,

Serial No. 614,091

17 Claims. 1

This invention relates to cementitiouscompositions and particularly to magnesium oxyohloride cements wherein seawater magnesia is employed.

In the past, the magnesia used in oxychloride cements has been obtained from magnesite ores, and whensaid magnesia has been used there has been no difiiculty in contraction as the cement sets. In fact, the problem hitherto has been to control the expansion of calcined "magnesite ore cements and not contraction thereof. :Ore of sufiiciently high quality for use in magnesium oxychloride cements is'becom'ingfidiflicult to obtain, whereas the supply of magnesia obtainable from seawater is practically inexhaustible. Oxychloa ride cement made from seawater magnesia-is stronger than that made from calcined ores-and in addition has almost a pure white color. The previous objection. has been that oxychloride cement made from seawatermagnesia shows excessive contraction (OB-0.5%). It is desirable that any additive to inhibit contraction be economical in cost and not reduce the strength of the cement to any extent. As anindication of the contraction of various magnesias and the effect of the additive it has been found:

Per cent contraction measured from hour after final set Per cent MgO from ore '0.10 -0.15 M O from seawater without additive 0.30 -0.50 MgO from seawaterwith additive 0.021-0-20 As an example, seawater magnesia may be obtained by removing calcium sulphate from the seawater bittern, reacting the bittern with lime or calcined dolomite, washing the resulting MgCOHh, filtering, and then calcining. Oxychloride cements made with seawater-magnesia have heretofore shown extensive contraction during curing after the-cement has set-which-invari ably leads to cracking of the cement and pulling away from the molds.- The excessive con-traction of these cements is attributable for the most part to the physical characteristics of, rather than the impurities in, the seawater magnesia,"whi'ch difier from those of conventional magnesia obtained from ore, as mag nesite, brucite and dolomite. An examination of seawater magnesia as conventiona-lly produced reveals. that it is a low bulk density white mass of particles pseudomorphic of magnesium hydroxide, having a bulk density of from so to l0 pounds-per cubic foot. In contrast thereto magnesia producedfrom ore is' ordinarily pseudomorphic of magnesium carbonate and usucements from magnesia of this low density char acter Whichwhen compounded with magnesium chloride solution and other conventional ingredients, as fillers, yields cements having excessive or prohibitive contracting tendencies, and the process involves mixing a, small amount ofla.

water soluble saltofa phosphoric acid having a lower proportion of combined molecules of water than orthophosphoric acid with such magnesia and with magnesium chloride-solution.-

f The phosphate salts constituting the additiuei j may be referred to collectively as the water soIuble salts of the phosphoric acids which contain less Water or a lower proportion of water molecules than orthophosphoric acid. The phosphoric acids of which the water soluble salts may besused include the pyrophosphoric, the meta.

phosphoric acids, and the polyphosphoric acids, the salts being employable in their monomeric or polymeric form. The salts and acids involved may be considered as molecularly dehydrated forms of the ortho salts and acids as distinguished from" the so-called dehydrationof phosphates by,

heating merely to drive off water of crystallization or the double-decomposition reactions char- 30' acterizing hydrolysis. For the purposes of this application sodium pyrophosphate may be considered to beapolyphosphate.

A preferred embodiment'of the invention contemplates making the addition of the contraction preventing, inhibiting, or reducing, material to the seawater magnesia after calcining but before addition of the magnesium chloride solution. The addition of water soluble salts of a phosphoric acid having a lower proportion of water molecules than orthophosphoric, preferably sodium pyrophosphate,.will substantially eliminate, inhibit, or reduce, to unobjectionable and small proportions, the contractioncommonly found in oxychloride cement made from seawater magnesia. Other water soluble salts h'aving'a lower proportion of water molecules than orthophosphoric acid have a similar action. Examples of other salts are sodium tripolyphosphate (Na5P'sOm), sodium tetrapolyphosphate, such as sold commercially under the trade name Quadrafos (Na6P4O1s), sodium acid pyrophosphate .(NazHzPzo'i) I v sodium-metaphosphate, '(NaPOs) and (NaPOsMf and NanPsOzv. As a further example, potassium pyrophosphate also may be used although it is not quite as effective in reducing contraction as some of the others.

In order to determine the effectiveness of some of the various substances, a series of tests was run as shown in Table I wherein a linear change bar was molded from the cement, said cement being approximately one part seawater magnesia, two parts silex, and five parts testing sand gauged with magnesium chloride solution, the contraction of the bar from one-half hour after final set to maximum contraction being determined with a micrometer. Sodium pyrophosphate was the particular additive selected for the tests but comparable results are obtained with the other additive. The contraction so obtained was compared with the contraction of the cement when no additive was used.

TABLE I E fiect of difierent phosphate 1 compounds on contraction and setting time of seawater M 90 C t t I 't' 1 F is t on rac H in 1a me e Additwe Used From t hour Set, min. min.

After Set None 0. 450 80 186 Nai'Pzoy (oyro) 0.037 93 193 Namom (tripolyphosnhate). 0. 044 120 260 NadrOn (Quadralos") o. 095 120 285 NauPsoz-l 0. 090 130 245 NSzHzPzO-r. O. 033 140 280 NaPOz. 0. 123 95 195 NaaROi 0. 320 135 280 K4PzO 0. 200 126 266 MESOA 0. 456 68 183 1 Also MgSOA TABLE II Efl'ect of varying amounts of sodium pyrophosphate on contraction of seawater oxychloride Per Cent Per Cent Expansion fi Contraction 7 From 16 hour After Set 1 day 3 days 7 days 1 Measured from maximum contraction.

It is noted that there is very little efiect in reducing contraction after the percentage reaches 1% and that about 0.25% at least must be added in order to obtain satisfactory results, the best range appearing to be between about 0.5% and 1%- This range holds generally for the other additives mentioned.

Strength tests run on seawater magnesia alone and with 0.5% (Mg0 basis) sodium pyrophosphate as an additive appear in Table III as compared with a typical calcined ore magnesia cement.

TABLE III Strength tests on oxychloride cement made from various samples of magnesia Modulus of Rupture, #/sq. in.

Typicl Magnesaia Seawater from Ore MgO+Pyro g% Dry Strength Age:

lday 1,053 1,120 900 Bdays 1,813 1,808 1,100 7 days 2, 393 2, 535 1, 300 21 days 2, 502 2, 470 l, 600

TABLE IV Efiect of varying amounts of sodium pyrophosphate on strength of seawater om chloride cement Transverse Strength, Amount #/sq. in. N34P207 Added 1 Day 4 Days Various specific mixes may be used for the cement, one of these, for example, being composed of about 25% MgO, 50% fine sand, 15% round lime rock, 5% asbestos, 5% FzOs, and 0.70% sodium pyrophosphate (MgO basis). Still another mix comprises 46 parts MgO, 7 parts fine sand, and 30 parts silex, together with 1 part sodium pyrophosphate. In mixes such as these, the material before initial set is quite fluid and the linear change characteristics relatively unimportant. Shortly after final set, however, the cement becomes quite rigid and in the period thereafter, maximum contraction is reached. As a result of this, the material pulls away from the sides of the mold appreciably and cracks will occur. In the case of magnesia derived from ore, the high expansion occurring after final set serves to counteract the initial contraction while in the case of seawater magnesia, very little expansion occurs.

Sodium pyrophosphate of C. P. grade or that made by fusing disodium orthophosphate at 1000 C. has been used as the additive with good results, such pyrophosphate exhibiting a concoidal fracture, single crystal orientation and being homogeneous.

- It has been established-"that the two reactions largely responsible for the formation: of oxychloride cement are:

Mgo+'Hzo Mg 0H)2 (1) and 3MgO+MgC12+ 1 IH2O93MgO" MgCh- 1'1H2O ;'I?he.linear change :ofxapaste, composed of seawater magnesiaand distilled 'waterwasimeasured with a: comparator: microscope and :the: material showed :.definite: contraction; totaling-more than 3,%"=with no later' expan'sion;cthusfshowing that reaction ('1)'"results..in 'ardecreaserin volume. A study made of the amount of slaking taking place when seawatertmagnesia with" and without sodium"-pyroph'osphate2 is agitated-with distilled water shows that 1% sodium pyrophospate almost completely 'stopstheslaking reaction.

1 Afteridrying with acetone andether.

In the'presence of sodium :pyrophosphate, reaction (1) is inhibited to a large extent, whilereaction (2) is not affected.

Sodium pyrophosphate obviously is converted to magnesium jpyrophosphate in the presence of as large an excess of MgO and MgClz as exists in an oxychloride cement mix. Experiments carried out'to determinewhether or not additionof magnesiumgpyrophosphate itself would control contraction showed that such was not the case. A sample or magnesium vpyrophospha'te was prepared by'dissolvingthepyrophosphate in water and adding MgClz solution-the precipitate filtered and dried overnight, and then' 1% (MgO basis) thereof was added'to a'mix, and the setting time and contraction determined in a second experiment. Sodium pyrophosphate was dissolved in water and added to the magnesium chloride in an amount such that 1% of sodium ,pyrophosphate (MgO basis) would be added in the form of magnesium pyrophosp'hate '(Mg2P2O7) tin suspension. Table showsthelres'ults obtainedx'and it is seen that-only "when the sodium: 'pyrophosphate added to the seawater magnesia: that satisfactor results occur. Thus the contraction and setting time effect depends upon the form in which the MgzlfzOv occursand to be effective in controlling contraction the magnesiumuayrophosphate must be precipitated in intimate contact with reacting MgO. This points towards the formation in situ of a protective filmaround the magnesia particles as'a possible mechanism by which contraction -isinhibited. It also has been found 'thatifthe additive is finely ground," such as" 200 meshfthe-material is more --effective.

TABLE Form of pyrophosphcte as additiveeflect on can.- tra ction and time of s t IDry. Freshly precipitated.

' The additives of the present'invention also may be used-to inhibit hydration of magnesium oxide, seawater and. other types, in other fields than Oxychloride cements such as inhibiting the thickening of a slurry of magnesiumoxide and other solid materials used in the fabrication of certain electrical insulators.

It is to be understood; of course, that the invention is not limited by an inadequate understanding of the theory of operation and that modifications may be made without departing from the spirit of the invention or the scope of the appended claims.

What is claimed:

' 1. The process of producing magnesia oxychloride cements which do not contractexcessively during curing,' from a magnesia derived by the calcination of magnesium hydroxide precipitated from a magnesium compound-in an-aqueous solution and which yields cements having prohibitive contracting tendencies when-t'compounded with" magnesium chloride solution? and fillers comprising, mixing a small"arnount 'sufficientito inhibit excessive contraction of a wateresoluble salt of a phosphoric acidhaving a lower'proportion of combined-molecules of water than orthophosphoric acid with magnesia having such property, with a fillerand with magnesium chloride solution.

2. The process "of producing magnesia oxychloride cements which do not contract excessively during curing, from a magnesia'='derived by the calcination of magnesium'hydro'xide precipitated from a magnesium compound'in an aqueous solution and which yields cements having prohibitive contracting tendencies when :compounded with magnesium chloride solution and fillers comprising, mixing a small amount sufficient to inhibit excessive contraction of a sodium salt of pyrophosp'horic acid with magnesia, having such property, with a filler and with magnesium chloride solution.

3. The-process of producing magnesia oxychloride cements "which do not contract excessively'during curing; from a magnesiaderived by the calcination 'of magnesium hydroxide precipitatd from a' magnesium compound in an aqueous solution and which yields cements having; prohibitive contracting tendencies when coming prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers comprising, mixing a small amount sufficient to inhibit excessive contraction of sodium acid pyrophosphate with magnesia having such property, with a filler and with magnesium chloride solution.

5. The process of producing magnesia oxychloride cements which do not contract excessively during curing, from a magnesia derived by the calcination of magnesium hydroxide precipitated from a magnesium compound in an aqueous solution and which yields cements having prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers comprising, mixing a small amount sufficient to inhibit excessive contraction of sodium polyphosphate with magnesia having such property, with a filler and with magnesium chloride solution.

6. The process of producing magnesia oxychloride cements which do not contract excessively during curing, from a magnesia derived by the calcination of magnesium hydroxide precipitated from a magnesium compound in an aqueous solution and which yields cements having prohibitive contracting tendencies when com pounded with magnesium chloride solution and fillers comprising, mixing a small amount sufiicient to inhibit excessive contraction of sodium tripolyphosphate with magnesia having such property, with a filler and with magnesium chloride solution.

7. The process of producing magnesia oxychloride cements which do not contract excessively during curing, which comprises mixing a small amount sufficient to inhibit excessive contraction of a water-soluble salt of a phosphoric acid having a lower proportion of combined molecules of water than orthophosphoric acid with low bulk density magnesia having a bulk density of 30 to 40 pounds per cubic foot obtained by the calcination of magnesium hydroxide precipitated from a magnesium compound in an aqueous solution and which yields cements having prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers, with a filler and with magnesium chloride solution. 8. The process of producing magnesia oxychloride cements which do not contact excessively during curing, which comprises compounding a small amount sufficient to inhibit excessive contraction of a water-soluble salt of a phosphoric acid having a lower proportion of combined molecules of water than orthophosphoric acid with low bulk density magnesia obtained by the calcination of precipitated magnesium hydroxide originating in natural waters and precipitated from an aqueous solution of a magnesium salt in aqueous solution and which yields cements having prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers, with a filler and also with magnesium chloride solution.

9. The process of preventing excessive contraction of magnesia oxychloride cement mixes having such tendency during curing, which comprises mixing a small amount sufficient to inhibit excessive contraction of sodium pyrophosphate with the magnesia employed in compounding the magnesia oxychloride cement mix, which magnesia is one, derived by the calcination of magnesium hydroxide precipitated from a magnesium compound in an aqueous solution and which yields cements having prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers.

10. The process of producing magnesia oxychloride cements which do not contract excessively during curing, from a magnesia derived by the calcination of magnesium hydroxide precipitated from a magnesium compound in an aqueous solution and which yields cements having prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers comprising, mixing a small amount sufficient to inhibit excessive contraction of a sodium pyrophosphate made by fusing disodium orthophosphate with magnesia having such property, with a filler and with magnesium chloride solution.

11. A slowly hydrating magnesia composition composed of finely divided magnesia obtained by the calcination of magnesium hydroxide precipitated from a magnesium compound in an aqueous solution and which yields cements having prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers and a small amount sufiicient to inhibitexcessive contraction of a water-soluble salt of a phosphoric acid having a lower proportion of combined molecules of water than orthophosphoric acid.

12. In the production of magnesia oxychloride cements from low bulk density magnesia derived by the calcination of magnesium hydroxide precipitated from a magnesium salt in aqueous solution and which yields cements having prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers, the method Of inhibiting excessive contraction of the cement during curing which comprises including in such cement mix a small amount adequate to inhibit contraction of a water-soluble salt of a phosphoric acid having a lower proportion of combined molecules of water than orthophosphoric acid.

13. A composition of matter for use in compounding magnesia oxychloride cements composed of sea water magnesia derived by the calcination of magnesium hydroxide precipitated from a magnesium salt in aqueous solution and which yields cements having prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers and a small amount sufficient to inhibit excessive contraction of a water-soluble salt of a phosphoric acid having a lower proportion of combined molecules of water than orthonhosphoric acid.

14. A composition of matter for use in compounding magnesia oxychloride cements composed of a magnesia derived by the calcination of magnesium hydroxide precipitated from a magnesium compound in an aqueous solution and which yields cements having prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers and a small amount sufficient to inhibit excessive contraction of a water-soluble, alkali-metal salt of a phosphoric acid having a lower proportion of combined molecules of water than orthophosphoric acid.

15. A composition of matter for use in compounding magnesia oxychloride cements composed of a magnesia derived by the calcination of magnesium hydroxide precipitated from a magnesium compound in an aqueous solution and I which yields cements having prohibitive contracting tendencies when compounded with magnesium chloridesolution and fillers and a small amount sufiicient to inhibit excessive contraction of a sodium salt of a phosphoric acid having a lower proportion of combined molecules of water than orthophosphoric acid.

16. A composition of matter for use in compounding f magnesia oxychloride cements composed of a magnesia derived by the calcination of magnesium hydroxide precipitated from a magnesium compound in an aqueous solution and which yields cements having prohibitive contracting tendencies when compounded with magnesium chloride solution and fillers and a small amount sufficient to inhibit excessive contraction of sodiumpyrophosphate.

1'7. A cdmposition of matter foruse in compounding-magnesia oxychloride cements, composed of a magnesia derived by the calcination of magnesium hydroxide precipitated from a 20 10 magnesium compound in an aqueous solution and which yields cements having prohibit contractingi, a-'te ndencies when compounded *{with magnesium chloride solution and fillers {and a small am t suflicient to inhibit excessive contraction of sodium tripolyphosphate.

.' WILLIAM C; EASTIN.

REFERENCES CITED 'lghe following references are of record in the file' of this patent: V UNITED STATES PATENTS Name Date Sullivan "Sept. 25, 1923 Sohl et a1 "June 20, 1944 OTHER REFERENCES;

Melldrs Modern Inorganic Chemistry, Revised Ed. 1939, (page 729). (Copy in Division 38.) 

1. THE PROCESS FOR PRODUCING MAGNESIA OXYCHLORIDE CEMENTS WHICH DO NOT CONTRACT EXCESSIVELY DURING CURING, FROM A MAGNESIA DERIVED BY THE CALCINATION OF MAGNESIUM HYDROXIDE PRECIPITATED FROM A MAGNESIUM COMPOUND IN AN AQUEOUS SOLUTION AND WHICH YIELDS CEMENTS HAVING PROHIBITIVE CONTRACTING TENDENCIES WHEN COMPOUNDED WITH MAGNESIUM CHLORIDE SOLUTION AND FILLERS COMPRISING, MIXING A SMALL AMOUNT SUFFICIENT TO INHIBIT EXCESSIVE CONTRACTION OF A WATER-SOLUBLE SALT OF A PHOSPHORIC ACID HAVING A LOWER PROPORTION OF COMBINED MOLECULES OF WATER THAN ORTHOPHOSPHORIC ACID WITH MAGNESIA HAVING SUCH PROPERTY, WITH A FILLER AND WITH MAGNESIUM CHLORIDE SOLUTION. 